1. Field of the Invention
The present invention relates to a discharge roller device which is disposed downstream of a fixing device in a paper transportation path of an image forming device.
2. Description of Related Art
A general fixing device includes a heat roller and a pressure roller which is pressed against the heat roller. When paper carrying a toner passes through a nip part between the heat roller and the pressure roller, the toner is heated and pressurized and the toner is fixed onto the paper. In such a fixing device, since the heat roller includes a heat source, the heat roller is maintained at a higher temperature than the pressure roller. Therefore, the paper that passed through the nip part is dewatered more on a surface of a side making contact with the heat roller than a surface of a side making contact with the pressure roller. Due to the difference in the dewatered amounts, fibers on the heat roller side shrink more than fibers on the pressure roller side. As a result, the paper curls.
A conventional discharge roller device discharges paper that passed through a fixing device to the exterior of an image forming device while correcting a curled direction of the paper. The conventional discharge roller device includes a mechanism which sags the paper in a width direction during the transportation of the paper. This mechanism is disposed downstream of the fixing device in the paper transportation path. Specifically, the conventional discharge roller device includes one roller pair or a plurality of roller pairs. In one of the rollers of a pair of rollers, a flange and a roller body are formed integrally. The flange sags the paper in the width direction. As described above, paper that has passed through the fixing device is discharged while the curl has been corrected.
A nip width is preferable to be wide for reliably discharging the paper. Therefore, at least one roller of the pair of rollers is a rubber roller having an elastic body. If a roller for driving (a driving roller) is formed as a rubber roller, the contact area of the driving roller and the paper at the nip part increases. Thus, the driving roller is preferable to be formed as a rubber roller.
In case a flange is provided on the driving roller, the flange strongly makes contact with the paper. If a sagged amount of the paper is excessive, there are cases in which a fold line is formed on the discharged paper. Therefore, there is a demand for the flange to sag easier than a contact portion of the pressure roller. In response to such a demand, in a conventional discharge roller device, a center part of a flange is hollow. However, the shape of the integrally formed rubber roller becomes complicated, and the length of the heat roller in the axial direction increases by the length of the flange. As a result, the manufacturing cost of the driving roller increases.
However, according to the present invention, without complicating the shape of the driving roller, the curl of the paper that has passed through the fixing device can be corrected.